1. Field of the Invention
The present invention relates to a character and image data (hereinafter referred to as "character/image data") reading system for a character/image data reading apparatus using solid image pickup elements, in which character/image data can be completely picked up even when the intervals of scanning lines are relatively large.
2. Description of the Prior Art
In general, a facsimile is so designed that, among a variety of scanning line densities, an optimum one is selected according to the kind of an original. When a scanning line density is selected, a scanning width (or an auxiliary scanning direction movement distance) required between reading of character/image data for one line and reading of character/image data for the next line is determined according to the scanning line density thus selected. The scanning width is set by increasing or decreasing the number of steps of a step motor for moving an optical system or an original, after the character/image data of each line have been read. For instance, in the case when the scanning width is minimum (or the scanning line density is maximum), the main scanning is carried out every step of the step motor; and in the case where the scanning width is maximum (or the scanning line density is minimum), the main scanning is carried out every four (4) steps of the step motor.
FIG. 1 shows various signal waveforms in the case where a character/image data reading apparatus with a CCD (charge coupled device) reads character/image data for one line every four steps of a step motor. When four motor pulses 11 for driving the step motor are produced as shown in FIG. 1(B) and the auxiliary scanning covers a distance corresponding to four steps as shown in FIG. 1(D), the movement in the auxiliary scanning direction is stopped and a start pulse 12 as shown in FIG. 1(A) is applied to the CCD, whereupon the CCD starts accumulating character/image data in the image accumulation region. In a time T.sub.1 (which is the character/image data accumulation time) the memory is enabled, so that the character/image data accumulated in the CCD is written into the memory. Thereafter, similarly as in the above-described case, character/image data for one line are read every four steps of the step motor.
It is assumed that the auxiliary scanning width is represented by A and the length, in the auxiliary scanning direction, of the light receiving window of the CCD is represented by B as shown in FIG. 2. In the case where reading character/image data (S.sub.0, S.sub.1, . . . ) for a line is carried out every four steps of the step motor, there is always a region C whose character/image data are not read unless the line density in the main scanning direction is changed according to the change of line density in the auxiliary scanning direction. Thus, the conventional character/image data reading system using solid image pickup elements suffers from a problem that, when the scanning lines are coarse in interval, character/image data cannot be completely picked up.